Method of reducing fading effects in radiocommunication



May 8, 1928. 1,669,219

A. H. TAYLOR I METHOD OF REDUCING FADING EFFECTS IN RADIO COMMUNICATIONFiled Feb. 17. 1927 IMIMI] INVENTOR. QEQI /Y d6 3 0 0,

ATTORNEYS.

Patented May 8, 1928 UNITED STATES PATENT OFFICE.

ALBERT H. TAYLOR, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO WIREDRADIO, INC., 01 NEW YORK, N. Y., A CORPORATION OF DELAWARE.

METHOD OF REDUCING FADING EFFECTS IN RADIOCOMMUNICATION.

Application filed February 17, 1927. Serial No. 169,045.

My invention relates broadly to signal transmission systems and moreparticularly to a system of transmission and reception wherein theundesirable effects of fading at receiving stations is substantiallyeliminated.

One of the objects of my invention is to provide a coordinated system ofhigh frequency transmission and reception by radio where reliability incommunication is assured independent of the effects of fading.

Another object of my invention is to provide a system of reception forhigh fre- 'quency transmission wherein continuous wave energy may besimultaneously received on identical radio frequencies but detected atdifferent audible frequencies and the signaling energy integrated at areceiver responsive to all of the difierent audio frequencies forinsuring reliable reception regardless of the fading of the signalenergy from one audible frequency to another.

My invention will be more fully understood from the specificationhereinafter following by reference to the accompanying drawing whichshows diagrammatically one form of the receiving circuit which may beemployed in carrying out the principles of my invention.

The most serious obstacle in obtaining results in radio communicationusing high frequencies, is the presence of fading which investigationhas shown is due to varying in- I terference patterns at the receivingantenna due to varying combination of incident waves coming from severaldirections at once. It is plainly seen that at remote receiving stationsthe wave energy arrives by a number of different routes having sufferedreflection from various portions of the Kennelly Heaviside layer (seeTaylor & Hulburt paper in Physical Review for February, 1926) thussending to the receiving antenna several electromotive" impulses whichvary in amplitude and phase, as the reflecting and absorbing mediumshifts about from moment to moment. These fading effects may be dividedroughly into two 0 asses; one, a rather rapid fading efi'ect, fastenough to be within the audible range and which averages outintelegraphy, although it may be very disastrous to telephony, and aslower fading effect of a number of seconds of duration.

I have found that if two antennae, separated by at least a considerablefraction of a wave length are used with the receivers, that the signalsdo not fade in and out exactly at the same time on these two receivers.However, the problem of fading is very much more difficult of solutionwith continuous wave transmission than with modulated continuous waveoperation.

An installation is representedin the draw ings having two antennae A andA and two single circuit regenerative receivers R and R which feed theiroutputs into the two primary windings 1 and 2 of the audio frequencydifferential transformer 3, the secondary winding 4 of which isconnected to a receiving telephone 5. H and H represent two separateheterodynes or drivers which may be used in the place of autodynereception, if desired. Consider first, the case of modulated continuouswave reception; the heterodynes will not be used and the regenerativereceivers R and R will not oscillate.

In this case the variations in intensity of modulated signals on the twoantennas A and A not being simultaneous, the telephones 5 will receive asort of average result which will show a good deal less fading thanreception from one antenna alone. Variations in the phase of the variouscomponents of the electromotive force received on the antenna at highfrequencies will not influence the phase of the resultantaudio frequencywhich is determined in the receiver. Therefore, the arrangement will beof benefit in vave reception then the phenomenze are entirely different.Assuming that each re ceiver R, and R is tuned to the incoming signaland that they either oscillate at synchrony, or if theyI do notoscillate, then the two heterodynes 1 and H must oscillate in.synchrony, or as a still further alternative, the one receiver or elsethe one heterodyne will supply the local oscillations for both. Thelocal osnillations will differ. by audible frequency from the incominghigh frequency signal. In this case, however, whenever the phase of theresultant electromotive force on antenna A shifts, as it usually shiftswhen fading, (if fading is an interference phenomena), then the shift ofthe audio frequency produced by the receiver R al. o shifts and by thesame amount in degree If the production of the beats between two highfrequencies differing by the audible frequency is considered, it isreadily observed that shifting the phase of either of the highfrequencies, will shift the phase of the resultant beat note which isobtained after rectification by the detector, and will shift it by thesame amount as the high frequency shift. The-same thing will happen inthe antenna A at the output of receiver R,. The two audio frequencies,therefore in two primary windings 1 and 2 of the di erential transformer3, are continuously shifting in phase with reference to each other asfading goes on differently in the two antwo receivers R, and

tennee A, and A Therefore, the fading on the whole, will not be reducedbecause there will be moments when these phases will be in opposition toeach other and the intensities will be approximately equal which willresult in the fading of signals. Under these conditions two antennae donotfunction any better than one antenna, and a very large number ofantennae do not improve results except in so far as the system becomesdirective by a suitable combination of antennae. It is possible,however, under many conditions to get a marked improvement in reception,using the arrangement shown in irrangements-can be made avoiding thisdifficulty of shifting hases by setting the 2 on slightly differentaudio frequencies, or if separate heterodynes are used, by oscillatingthem on different frequencies. The receivers actually receive the samefre uency but the circuits are offset so that the cat tones aredifferent. For instance, suppose the receiving frequency is 4000kilocycles, and one heterodyne is set at 3999 kilocycles, and the otherone is set at 4001.2 kilocycles. The two primary windings .1 and 2differential transformer 3 will then receive, due to the rectificationin R, a beat frequency of 1200 cycles and due to the rectification in Ra beat frequency of 1000 cycles. These two frequencies can not combinevectorially for neutralization. They will in general, give a double tonein the receiver 5 and as fading goes on, one tone or the other willpredominate but the average readibility will be greatly improved. It maybe objected at once that the two heterodynes, or autodynes, ifheterodynes are not used, will give a difference frequency of 2200cycles which 'would be very would drown out all signals. y way ofexample, suppose the receiving frequency is 8000 kilocycles. Onereceiver is set on 8001 kilocycles and the other on 8001.3 giving a beatnote of 1000 cycles and 1300 cycles re-- spectively, on the sameincoming signaling frequency. This is avoided by providing a tone filteror audio frequency trap 6 in .the circuit to the telephones 5 so as totrap out this undesirable frequency which is considerowerful and ventionare intended other than are imposed by the scope of the appended claims.

. What I claim as new and desireto secure by Letters Patent of theUnited States is as follows:

1. A receiving system for high frequency signals comprising a pluralityof radio frequency energy collecting circuits, separate receivingcircuits coupled with said radio frequency energy collecting circuits,said radio frequency collecting circuits being separated by at least aconsiderable fraction of the wave length of the transmittedsignals,independent high frequency oscillators connected with each of saidreceiving circuits, said oscillators being arranged to operate atslightly separated frequencies, a common output circuit for saidreceiving circuits and a responsive device coupled to said common outputcircuit whereby signaling energy over a band of audio frequenciesprovided by said radio frequency energy collecting circuits actuate saidresponsive device.

2. In a system for reducing the effects of fading in high frequencysignal transmission systems a receiving apparatus including in- Idependent radio frequency energy collecting circuits, each of saidcircuits being separate at least a considerable fraction of the wavelength of the transmitted signals, independent receiving circuitsconnected to said separate radio'frequencyenergy collecting circuits, aresponsive device, a circuit common to each of said receiving circuits,connections between said common circuit and said responsive device andseparate high frequency generators coupled with said receiving circuitsand each operative at slightly separated frequencies for combining theeffects of signaling energy over a band of audio frequencies in saidcommon circuit for controlling said responsive device.

3. A receiving system for reducing the effects of fading comprisingaplurality of antenna systems separated one from the other for at least aconsiderable fraction of the wave length of the transmitted signals, a.

receiving circuit connected with each of said antenna systems, separategenerators of high frequency current/coupled to each of said 4. In asystem for reducing the efiects of fading in radio reception thecombination of a pair of separate antenna systems separated one from theother for at least a considerable fraction of the wave length of thetransmitted signals, independent receivers connected with said antennasystems, separate generators of high frequency energy coupled with eachof said receivers, adifferential transformer system having a air ofprimary windings and a single secon my windin' connections between theoutputcircuits of said receivers and the rimary windings of saiddifferential trans ormer system, a responsive device, and connectionsbetween said secondary device whereby the combined effects of saidgenerators and signaling energy incident upon said separate antennasystems actuate said responsive device.

ALBERT H. TAYLOR.

winding and said responsive

